Katie Couric couldn't help "Good Morning America" narrow its ratings gap with NBC's top-rated "Today" on Monday, much less close it.

"Today" averaged 4.903 million total viewers, 496,000 more than "Good Morning America," as Couric started a weeklong stint as a "GMA" guest anchor. That was almost exactly in line with the half-million viewers by which "GMA" typically lags the top-rated "Today."

Among 25 to 54-year-olds — the demographic most important to news show advertisers — "Today" had a 1.9 rating compared to a 1.5 rating for "GMA." That reflected 2.273 million viewers in the demo, 482,000 more than "GMA."

Both shows — despite the addition of Couric on "GMA" and Meredith Vieira on "Today" — were down from their seasonal averages. That suggested that other factors, including perhaps Oprah Winfrey's appearance on "CBS This Morning," cut into their numbers.

"GMA" has averaged 4.9 million viewers this season, while "Today" has averaged 5.4 million. "CBS This Morning" has averaged 2.5 million.

CBS' Monday numbers were not released Tuesday.

ABC and NBC's Monday ratings were available because both networks ordered special expedited ratings from Nielsen, and CBS did not.

The continued ratings success of "Today" — the show Couric anchored until 2006 with Matt Lauer — set the stage for another ratings matchup Tuesday, this time between "GMA" and a "Today" show guest-hosted by Sarah Palin. Palin started the show by sitting surrounded by newspapers, a joke about her flubbed answer to a question Couric asked her in a 2008 interview.

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